Organophosphorus compounds are well known in the art as agricultural insecticides. Organophosphorus compounds have been formulated both as liquid and as solid products. The solid formulations have been sold as both powders and granules; however, the granular form is most commonly used today.
Organophosphorus insecticides are relatively unstable molecules and tend to decompose readily, particularly when exposed to high or low pH. Furthermore, organophosphorus compounds will undergo hydrolysis in the presence of water. Thus, it is known in the prior art that the chemical stability of solid formulations of organophosphorus insecticides can be enhanced by the addition of certain materials that reduce the rate of chemical degradation of the active ingredient.
U.S. Pat. Nos. 4,380,537; 5,140,019; 5,165,934 and 5,260,312 all disclose organophosphorus insecticides on solid carriers, such as clays. Specifically, U.S. Pat. No. 4,380,537 discloses an insecticide formulation containing an organophosphorus insecticide, such as chlorpyrifos, on a clay carrier, such as montmorillonite or attapulgite, and as a stabilizer for the insecticide between 0.5% and 10% by weight of a lactone. Other stabilizers of organophosphorus insecticides known in the prior art include polyethyleneglycol and polypropyleneglycol. W. Kelley et al., "Use of Deactivators in Granular Clay Formulations," discloses the use of ethanolamine, ethyleneglycol (and dimers thereof), propyleneglycol (and dimers thereof), and urea as deactivators for formulations of pesticides on clay-based granules. However, the stabilized insecticidal formulations of the prior art have not always been satisfactory.
A formulation of 15% by weight chlorpyrifos on a granular clay carrier and 4.5% by weight of dipropyleneglycol as a stabilizer is unsatisfactory for agricultural use upon cold storage. After storage at relatively cold temperatures, the granules will agglomerate and form hard lumps that make the formulation unsuitable for agricultural application using conventional equipment. Heretofore, it has not been known how to stabilize granular formulations of organophosphorus insecticides against agglomeration or clumping that result from cold storage.
Therefore, a need exists for an improved cold storage stabilized organophosphorus insecticide formulation.